Method for detecting a rollover situation

ABSTRACT

The invention relates to a method for detecting a rollover situation in such a way that a restraint, such as belt tighteners or head airbags, can be released at the right time during rollover. The signals that pertain to several sensors and detect transitional and rotational movements are detected, connected to one another and evaluated.

CLAIM FOR PRIORITY

This application claims priority to International application No.PCT/DE01/00293 which was published in the German language on Sep. 7,2001.

TECHNICAL FIELD OF THE INVENTION

The invention relates to a method for detecting a rollover situation.

BACKGROUND OF THE INVENTION

Previous systems only compare the sensor signals provided by the sensorsfor detecting a rollover situation with a fixed threshold or only setsensor signals from sensors of the same type against one another. Acombination of these sensor signals and a comparison with a thresholdvalue is used to decide upon a triggering of the restraint means, whicheither leads to a high sensitivity of response and correspondingspurious triggerings (misuse) or leads to the triggering decision notbeing made at the right time.

SUMMARY OF THE INVENTION

In one embodiment of the invention, sensor signals are linked with athreshold value and one another to perform a triggering decision if asensor signal exceeds the threshold value.

This enables a restraint device, such as belt tensioners or airbags, tobe triggered at the right time in the case of a vehicle rollover.

The detection of a rollover situation is carried out in the preferredembodiment by the calculation of suitable terms from the rate ofrotation, the lateral and the vertical acceleration of the vehicle. Therate of rotation can be detected by a sensor, which detects the movementand/or the change of movement about one of the longitudinal axes, forexample the longitudinal and/or transverse axis of the vehicle. Theterms suitable for detecting the rollover situation include theacceleration values of at least one direction and are linked with therate of rotation term to form a dynamic threshold. This dynamicthreshold is compared with a criterion derived from the rate ofrotation.

The invention has at least the following advantages:

-   -   No spurious triggering in the case of a sensor fault due to a        two-out-of-three decision.    -   Detection of a vehicle rollover before reaching the dynamic        toppling threshold of the vehicle;    -   Evaluation of the rotation and translation of the vehicle;    -   Detection of the circumstances of rotation and translation        typical for a vehicle rollover situation and thus a robust        behavior in a misuse situation and in situations in which the        vehicle comes close to the dynamic toppling angle;    -   Estimation of the movement of the occupant in the case of        vehicle rollovers which are preceded by a driving situation with        a large lateral inclination. If it is detected that, due to a        large inclination, the occupant is in the unfolding zone of an        airbag (head airbag, curtain), then the airbag will not be        activated under any circumstances;    -   Separate activation of side airbags depending on the direction        in which the vehicle rolls over. If further airbags are needed        due to rotations >180°, then these are activated as required;    -   Adaptable to suit different vehicle types (van, SUV, . . .) and        different restraint systems (belt tensioners, curtain/head        airbags, roll bar) due to the ability to set parameters;    -   If an acceleration sensor fails, at least some of the possible        vehicle rollover scenarios can be detected with the remaining        acceleration sensor.

In one aspect, a rate of rotation signal and an acceleration signal areset against a triggering threshold, which is equivalent to mixing ofdifferent physical variables.

In another aspect, a dynamic threshold is calculated from the rate ofrotation signal and an acceleration signal.

Essentially, two types of rollover accident occur:

In a “tripped rollover”, the vehicle skids sideways in the direction ofits transverse axis (Y-axis) and rolls over after catching on a lateralobstruction, for example the edge of a curb stone.

In an “untripped rollover”, the vehicle travels sideways down anembankment and rolls over on exceeding the lateral toppling angle of thevehicle about its longitudinal axis (X-axis).

Determined by the type of rollover (tripped or untripped), in additionto the rate of rotation signal, the appropriate acceleration signal ofthe sensors aligned in the direction of the Z-axis or the Y-axis isautomatically selected and becomes operative.

Two sensor signals are used to make the triggering decision. The, atleast two sensor signals are also used to provide a safing function atthe same time. Safing means that a spurious triggering as a result offaulty components, e.g. of a sensor, is prevented. A triggering withonly one sensor signal is not possible, which prevents undesiredtriggering from occurring in the event of a single fault with onesensor.

The two acceleration sensors, Y and Z, which detect accelerations in thedirection of the Y-axis and the Z-axis of the vehicle, respectively, arenot taken into account together and can also not bring about atriggering decision. The rate of rotation signal of one rate of rotationsensor represents the angular speed, from which the angle of inclinationof the vehicle is also formed by integration. The rate of rotationsignal alone is not sufficient for the triggering, regardless of thevalue of this rate of rotation signal or the angle of rotation.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained with reference to the figures. In thedrawings:

FIG. 1 shows a simplified block circuit diagram for evaluating thesensor signals of a restraint system.

FIG. 2A shows a vehicle situation, represented by the time-relatedsequence of the sensor signals and the threshold values derived fromthem, which lead to a decision not to trigger (non-deploy).

FIG. 2B shows a vehicle situation, represented by the time-relatedsequence of the sensor signals and the threshold values derived fromthem, which lead to a decision to trigger (deploy).

FIG. 3 shows a block circuit diagram of an appropriate safing concept.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, sensors Y, Z for the detection of vehicle accelerations inthe vehicle transverse axis (Y-direction) and the vertical vehicle axis(Z-direction) and a rate of rotation sensor AR for detecting the speedof rotation of the vehicle about the vehicle longitudinal axis (X-axis)are shown. The signals from the sensors Y, Z, AR are evaluated by athreshold value generator SB, which forms a dynamic rollover threshold Sin accordance with a predefined algorithm. A matching element Adetermines the angular speed W about the vehicle longitudinal axis fromthe signal of the rate of rotation sensor AR. A comparator V, which canbe arranged in an airbag control unit ECU, for example, sends a firingcommand F to a downstream restraint means when the angular speed Wexceeds the rollover threshold S.

The device shown in FIG. 1 is part of an occupant restraint system of avehicle, for example.

Different vehicle situations are shown in FIGS. 2A and 2B:

The vehicle inclination β about the longitudinal axis (X-axis) of thevehicle as a function of the time t is represented by the dotted graph.The units of the vehicle inclination are given in degrees (°).

The angular speed W (rollover criterion) of the vehicle about thelongitudinal axis of the vehicle as a function of the time t isrepresented by the dashed graph. The units of the angular speed W aregiven in degrees per second (°/s). The angular speed W represents thecriterion for the detection of a rollover (rollover criterion W).

The dynamic rollover threshold S (rollover threshold) is calculated fromthe signals of the acceleration sensors Y, Z in the Y- and Z-directionand of the rate of rotation sensor AR and is represented by thecontinuous graph. The units of the rollover threshold S are converted todegrees per second (°/s).

The output signal of the rate of rotation sensor AR detects the rotarymovements about the X-axis of the vehicle and is preferably filtered bya low-pass filter. The signal present at the output of the low-passfilter represents the angular speed W, which is integrated by means ofan integrator in order to obtain the vehicle inclination β.

If the rollover criterion W exceeds the dynamic rollover threshold S(rollover threshold), then a rollover is detected and the restraintdevice is triggered.

The rollover threshold S is reduced on the occurrence of lateralaccelerations in the y-, z-direction and/or rotary accelerationspredominantly about the longitudinal axis of the vehicle.

A critical vehicle situation, resulting from a bend being taken tootightly for example, is shown in FIG. 2A, in which the vehicle inclineslaterally with high angular acceleration (W max=130°/s) and strongly byabout β=20° (t=0 to 400 ms) and then catches itself again, however,after lateral compensatory movements about the longitudinal axis (t<400ms). The rollover threshold S is reduced during the period 150 to 300ms, mainly due to the lateral acceleration terms. No significantacceleration occurs in the z-direction. However, as the rollovercriterion W does not exceed the threshold S, no restraint system istriggered (non-deploy).

An accident situation is shown in FIG. 2B, in which the vehicle goesinto a sideways skid (t=50 ms), begins to incline sideways (t=75 ms) andis then abruptly braked by an unevenness in the highway (t=100 ms), as aresult of which the vehicle begins to roll over about the X-axis (t>100ms). The vehicle comes to rest at an angle of about β=90° (t>1500 ms).The algorithm detected at an early stage (t=100 ms) that the vehicle wasbeing braked so strongly and, at the same time, inclined in the lateraldirection that this would lead to a rollover. The decision to fire isreached at the moment in time at which the rollover criterion exceedsthe dynamic rollover threshold S.

Due to the strong lateral acceleration in the y-axis, the rolloverthreshold S reduces for a short time to 100°/s, as a result of which theangular speed w exceeds the rollover threshold S. Consequently, thetriggering decision (deploy) is taken.

Furthermore, it can be seen that, from about t=600 ms, changes in theacceleration occur along the z-axis, which lead to a continuousreduction in the rollover threshold (t=600 . . . 1000 ms) . If thevehicle were not to come to the lateral position w=90° due to a stronglateral acceleration in the Y-direction but due to traversing anembankment with slow lateral inclination, the restraint means wouldtrigger at about time t=800 ms (intersection of the graphs w-S).

In this way, widely differing accident situations and “only” criticalvehicle situations are clearly detected and the restraint meanstriggered or not at the correct point in time.

A safing concept is shown in FIG. 3, with which the lateral accelerationin the y-axis and the vertical acceleration in the z-axis are ORedtogether and the result of the OR operation is ANDed with the angularacceleration w of the rate of rotation sensor AR. This ensures that aspurious triggering does not take place in the case of a defectivesensor.

1. A method for detecting a rollover, comprising: detecting atranslatory movement and a rotary movement of the vehicle; determining arollover threshold, wherein the rollover threshold is dependent on a)acceleration of the vehicle in the vertical direction, b) accelerationof the vehicle perpendicular to its longitudinal axis, and c) the rotarymovement of the vehicle and triggering a restraint device if the rotarymovement exceeds the rollover threshold.
 2. The method as claimed inclaim 1, wherein the rollover threshold depends on the acceleration ofthe vehicle perpendicular to a vehicle axis.
 3. The method as claimed inclaim 1, wherein the rollover threshold depends on an angular speed ofthe vehicle about a longitudinal axis.
 4. The method as claimed in claim1, wherein the rollover threshold depends on the acceleration of thevehicle in a vertical direction.
 5. The method as claimed in claim 1,wherein the rollover threshold depends dynamically on at least one of aduration in time of an acceleration of the vehicle perpendicular to avehicle axis and an angular speed of the vehicle about a longitudinalaxis and the acceleration of the vehicle in a vertical direction.
 6. Themethod as claimed in claim 1, wherein a further sensor detectsacceleration in a vertical direction.
 7. The method as claimed in claim1, wherein the restraint device triggers when at least one accelerationsignal and at least one rate of rotation signal is present.